1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to wireless communication technology, and more particularly to a data structure for transmitting large amounts of multimedia content.
2. Description of the Prior Art
Because of the current trend towards wireless networks, and the increase in demand for transmission of large amounts of multimedia data, there has been an increasing demand for research on more effective transmission methods in a wireless network environment. Moreover, it is now increasingly necessary to wirelessly transmit high quality video such as Digital Video Disk (DVD) video and High Definition Television (HDTV) video among various home devices.
Presently, one task group of the IEEE 802.15.3c is pursuing the establishment of a technical standard for transmitting large amounts of data in a wireless home network. This standard, which is referred to as Millimeter Wave (mmWave), uses radio waves having a millimeter wavelength (i.e., radio waves having a frequency of 30 to 300 GHz) for transmission of large amounts of data. Up to now, such a frequency band was an unlicensed band limited to communication providers, radio wave astronomy, vehicle collision prevention, and others.
FIG. 1 is a diagram comparing the frequency bands of the IEEE 802.11 series standards and mmWave. The IEEE 802.11b or IEEE 802.11g uses a carrier frequency of 2.4 GHz and has a channel bandwidth of about 20 MHz. Further, IEEE 802.11a or IEEE 802.11n uses a carrier frequency of 5 GHz and has a channel bandwidth of about 20 MHz. However, mmWave uses a carrier frequency of 60 GHz, and has a channel bandwidth of about 0.5 to 2.5 GHz. Herein, it should be noted that the mmWave has a carrier frequency and a channel bandwidth much higher and much wider than those of the existing IEEE 802.11 series standards. By using high frequency signals (millimeter wave), it is possible to obtain a very high data rate of several Gbps, and to reduce the antenna size to less than 1.5 mm, and it is thus possible to create a single chip including an antenna. Further, since the attenuation ratio in air is very high, it is also possible to reduce interference among devices.
Recently, research has been conducted in order to transmit uncompressed audio or video data (hereinafter, referred to as uncompressed AV data) among radio devices by using the high bandwidth of the millimeter wave. Compressed AV data is lossy-compressed through motion compensation, DCT conversion, quantization, variable length coding, and others, in such a manner that portions less sensitive to human visual and auditory senses are removed. However, the uncompressed AV data include digital values (e.g. R, G and B components) representing pixel components.
Accordingly, bits included in the compressed AV data have no priority according to importance, but bits included in the uncompressed AV data have a priority. For example, as illustrated in FIG. 2, in the case of an 8 bit image, one pixel component is expressed by 8 bits. Of them, a bit (bit of the highest level) expressing the highest order is a Most Significant Bit (MSB), and a bit (bit of the lowest level) expressing the lowest order is a Least Significant Bit (LSB). That is, respective bits in one byte data including 8 bits have different levels of importance in restoring image or voice signals. If an error occurs in a bit with a high importance during transmission, error occurrence can be more easily detected as compared to the case where an error has occurred in bits with low importance. Accordingly, bit data with high importance must be greatly protected in order to prevent an error from occurring therein, in a different way from bit data with low importance. However, as with the conventional transmission scheme of IEEE 802.11 series, an error correction scheme and a retransmission scheme with the same coding rate for all bits to be transmitted have been used.
FIG. 3 is a diagram illustrating the structure of a physical layer (PHY) Protocol Data Unit (PPDU) of the IEEE 802.11a standard. The PPDU 30 includes a preamble, a signal field and a data field. The signal field includes a rate field representing a transmission rate, a length field representing the length of the PPDU, and others information. Typically, the signal field is encoded by one symbol. The data field includes a PSDU, a tail bit and a pad bit, and data to be actually transmitted is included in the PSDU.
The conventional frame format as described above may be effective in general data transmission. However, in order to transmit large amounts of data at several Gbps in an ultra-short distance of about 10 m, new header and frame structures must be considered. Specifically, as the main application field of wireless transmission technology transmitting data at several Gbps, in order to transmit uncompressed audio/video data (hereinafter, referred to as uncompressed AV data), it is necessary to design header and frame structures in consideration of error correction and retransmission schemes based on the importance of data as described above.